Subsea power line communication is a special form of underwater communication. It is preferably used in exploring and exploiting gas and oil fields located at the seabed. Subsea communication is used, for example, for transmitting various data between topside control sites and subsea wellheads. Gas and oil fields that are explored or exploited using electronic communication to the wellheads or to other electronic equipment are sometimes called “electronic fields” (e-fields).
In prior art, different techniques for subsea communication have been described. On the one hand, there are wired electric or optical connections, on the other hand there are wireless connections. The wired connections can be subdivided into a first group providing communication lines for electronic or optical connections separate from electric power lines, and a second group utilising power lines for electronic communications. In the latter case, advantageously no separate communication lines are needed.
For example, in US 2005/0243983 A1, a modem for receiving and transmitting data from and to a conductor is described. It comprises an output drive for transmitting data to the conductor, a receiver for receiving data from the conductor and impedance matching means for matching an impedance of a receiver input with an impedance of the conductor. A gain of the output drive, a receiver gain and the impedance of the receiver input are adjustable at this modem.
All known modems for subsea power line communication use some kind of frequency shift keying modulation technique, allowing for bit rates of up to 19200 bit/s and operational ranges of up to about 100 km. For this purpose, the known modems make use of diplexers comprising a low-pass filter for the electric signal and a high pass filter for the modulated binary data, filtering out frequencies above and below 100 kHz, respectively.